Turbine aircraft engines are started by beginning engine rotation, introducing fuel at a proper time to achieve ignition, and accelerating the engine to a self-sustaining ground idle condition. The whole process is commonly known as the start cycle. An electric starter or starter/generator is used to initially rotate the engine and accelerate it to the point where it runs under its own power.
During the time between initial engine rotation and fuel ignition, the engine does not experience a meaningful amount of temperature-induced stress. However, at the point of ignition through acceleration to ground idle, the engine does experience a meaningful amount of temperature-induced stress. In fact, the stress experienced by the engine during this time is greater than the stress experienced during takeoff and flight. Hence, it is desirable to reduce the time exposure within the engine start cycle between ignition and ground idle. It is also desirable to reduce the temperature which is seen by the engine during this time.
One solution to reducing the engine's start cycle duration might be to accelerate the engine as rapidly as possible through the start cycle beginning with initiation of the start cycle. This however poses some problems which are equally if not more stressful on the engine. One might, for example, initially supply the starter with all of the power necessary for the starter to take the engine through the entire start cycle. Doing so does not meaningfully improve the quality of the start and can stress electrical components including the starter, which are susceptible to heat damage caused through the dissipation of excess current and engine torque. Over a period of time, such electrical and engine components can wear out prematurely and require replacement. It would be ideal to have an engine start system which is sensitive to the engine start cycle and can react and manage the cycle for efficient and low-stress engine starts.
This invention arose out of concerns associated with providing a starter system for a turbine aircraft engine which monitors and manages the start cycle to produce a more efficient start with less stress to the engine.